1. Technical Field
The present invention relates to a television-connection-state detecting device that makes detection as to whether a television set is connected to its television connection terminal or not. In addition, the invention further relates to an image display device that is provided with such a television-connection-state detecting device.
2. Related Art
Some electronic devices such as a photo-printer, a digital camera, and the like are provided with a small-sized image display unit such as a liquid crystal display or the like. Some users have a need for connecting such an electronic device to an external television (hereafter may be abbreviated as “TV”) set that has a larger size of a display screen than that of the built-in image display unit thereof so as to obtain a larger picture. In such an application, from the viewpoint of user-friendliness, it is preferable that an electronic device can automatically detect the connection of an external television set; that is, it is preferable for the electronic device to be capable of making a self judgment as to whether a television set is connected to its television connection terminal or not. A television-connection-state detecting device of the related art that is described in, for example, JP-A-7-311639 performs automatic TV-connection-state detection as follows. That is, the related-art TV-connection-state detecting device described in JP-A-7-311639 compares the signal level of the TV connection terminal of an electronic device and the level of a reference voltage. Then, on the basis of the result of comparison, the related-art TV-connection-state detecting device described in JP-A-7-311639 outputs a detection signal.
However, the presence/absence of an external television set connected thereto is not directly detected in the TV-connection-state detecting technique disclosed in the above-identified patent publication because, as explained above, it merely compares the signal level of the TV connection terminal of an electronic device and the level of a reference voltage. For this reason, disadvantageously, there is a risk of erroneous detection of the presence of an external television set connected thereto even when, for example, not a TV set but a cable is connected to the TV connection terminal of an electronic device because the signal level of the TV connection terminal thereof changes due to the connection of the cable to the TV connection terminal thereof.